It is well known that ketene dimer compounds react and combine with hydroxy groups of cellulose fiber molecules to size cellulose fibers. Recently, they are particularly noted as a sizing agent for paper which can be used for paper-making in a neutral or slightly alkaline range without using alum.
Ketene dimer compounds have heretofore been being marketed and used in the form of an aqueous dispersion in which they are dispersed in an aqueous continuous phase containing starch, especially cationized starch. However, it is very difficult to obtain a stable aqueous dispersion of ketene dimers, since they are inherently highly reactive with water. A dispersion system will lose its homogeneity, for instance, forming scum or being gelled during storage. Further, the sizing efficiency and water-proofing property may deteriorate during storage. Especially, it is very difficult to obtain a stable high ketene dimer concentration aqueous dispersion thereof, and therefore the concentration of ketene dimers in conventional ketene dimer aqueous dispersions commercially available today is 15% at the highest. Such low concentration dispersion products are obviously disadvantageous in transportation and storage. Further, even such low concentration dispersions do not always have sufficient storage stability and therefore are not satisfactory for users.
The object of this invention is to provide a ketene dimer aqueous dispersion which has excellent storage stability at a concentration of not less than about 25% and is satisfactory in practical use. Of course, a ketene dimer aqueous dispersion of this invention effectively sizes cellulose fibers.